The field of the invention is methods and apparatus for managing the cooling of electrical devices and electronic components in larger systems such as an electric vehicle.
The greenhouse effect and the concern over decreasing energy resources imposes a huge demand on hybrid electric and fill electric vehicle designs. Thermal management considerations must include the heating and cooling of the components of the vehicle as well as the passengers"" environmental comfort levels.
Innovations in the thermal management of semiconductor devices used in power electronics have been limited. Methods for dissipating large quantities of heat have traditionally been restricted to passive cooling techniques, channel cooling, solid heat sinks, or use of fans. With the advent of larger, faster, higher current semiconductors, efficient cooling methods are required to dissipate ever-increasing amounts of waste heat. It is estimated that 55% of electronic product failures are due to excessive temperatures. Universities and industry are currently working to develop new methods to provide thermal management for circuit board assemblies as well as individual silicon dies.
The cooling in the thermal management of a vehicle is currently conducted in a piecemeal fashion. Separate cooling systems are used for the vehicle passenger compartment, the motor and the electronic devices.
New methods of cooling electronic components have also recently been proposed. Promising new technologies being examined include immersion cooling, jet impingement and spray cooling. Dielectric fluids with high heat capacities and advantageous electrical characteristics are being investigated to work with these new xe2x80x9ctwo-phasexe2x80x9d technologies. New thermosyphon cooling techniques are being applied to electronics at both circuit board and individual chip levels.
In one such method, the semiconductors are immersed in a dielectric which vaporizes as the chips increase in temperature. The vapor condenses as it rises and is cooled by a water pipe, changes back to liquid phase, and then drops back into the pool. The temperature difference between the vapor and the liquid is negligible. For a lower vapor temperature, the water-cooled heat exchanger is comparatively large for a given heat extracted from the multichip modules.
In another arrangement, the semiconductor chips are not totally immersed in the dielectric fluid. Downward movement of the liquid is caused by gravity. On system start-up, the pump must initially be turned on to fill the reservoir before energizing the chips.
Other methods of cooling semiconductor components include impingement by jets of cooling liquid, as well as cooling by spraying a coolant directly on the chips. In both cases the liquid can be vaporized, cooled, returned to a liquid state and recirculated.
A thermosyphon assembly may be used to implement a two-phase liquid cooling system by indirect contact with electronics. In this system the density difference between the liquid and vapor creates a pressure head, which drives the flow through the loop so no driving force is needed. This method is being used to dissipate heat from PC processors.
Research is being performed in spray cooling of IGBT power switching devices with results of up to 34% improvement seen in their power handling capabilities. Water is being utilized as the coolant in these systems with the semiconductors coated with a conformal dielectric. Additionally, the technology involves the construction of the nozzle array from silicon by reactive ion etching.
Yet another approach for cooling semiconductors involves heat pipes imbedded in an evaporator. A heat pipe includes a vacuum tight envelope, a wick structure and a working fluid. The heat pipe is evacuated and then back-filled with a small quantity of working fluid. The atmosphere inside the heat pipe is set by an equilibrium of liquid and vapor. As heat enters the evaporator, the equilibrium is upset generating vapor at a slightly higher pressure. This vapor travels to the condenser end where the slightly lower temperatures cause the vapor to condense giving up its latent heat of vaporization. The condensed fluid is then returned to the evaporator through capillary action developed in the wick structure. This continuous cycle transfers large quantities of heat with very low thermal gradients. A heat pipe""s operation is passive, being driven only by the heat transferred.
Heat pipes have been embedded in power amplifier modules. In one application the heat pipes were 0.375xe2x80x3 in diameter and flattened into grooves in the heat sink base with a thermal epoxy at the interface. This approach reduces the thermal resistance of the heat sink by 50%.
In loop thermosyphons, a circuit board is essentially immersed in the coolant and vapor chambers. A vapor chamber is a vacuum vessel with a wick structure lining the inside walls that is saturated with a working fluid. As heat is applied, the fluid at that location immediately vaporizes and the vapor rushes to fill the vacuum. Wherever the vapor comes into contact with a cooler wall surface it will condense, releasing its latent heat of vaporization. The condensed fluid returns to the heat source via capillary action, to be vaporized again and repeat the cycle. The capillary action of the wick enables the vapor chamber to work in any orientation with respect to gravity. A vapor chamber heat sink consists of a vapor chamber integrated with cooling fins and pins. Due to the way the vapor chamber operates, the heat source can be placed anywhere on the base without affecting its thermal resistance. In addition, there can be multiple heat sources dissipating the same or different amounts of power. The rate of fluid vaporization at each source will stabilize and the vapor chamber will be nearly isothermal.
The cooling approaches discussed above are solving thermal problems in a piecemeal fashion. The present invention solves the cooling and heating problems of hybrid and full electric vehicles from a system approach. In doing so, the system may be designed so that individual electrical devices and mechanical components perform multiple functions. This results in a lower cost, smaller volume, and higher efficiency system.
The invention provides a total thermal management system that includes heating and cooling of critical electrical and electronic components as well as controlling the temperature of the passenger compartment of a vehicle.
The invention provides a total thermal management system that shares hardware for multiple functions.
The invention provides a total thermal management system for hybrid electric vehicles.
The invention provides a total thermal management system for full electric vehicles.
The invention provides a total thermal management system that shares a digital signal processor (DSP) for monitoring and control functions as well as controlling an inverter.
The invention provides a total thermal management system that shares a compressor and condenser for multiple thermal management functions.
The invention provides a total thermal management system that shares an inverter for multiple functions. For example, the invention provides for an inverter controlling both a traction motor and a compressor motor.
The invention provides a system for cooling dies of power semiconductors and an inverter which will withstand the start up conditions of the system.
The invention provides for direct cooling of motors with shaft seals.
The invention provides for indirect cooling of motors without shaft seals.
One embodiment of the invention is an integrated thermal management system having; a refrigeration subsystem having a refrigerant and multiple components, an electrical subsystem having multiple components, an electronic control subsystem having multiple components, wherein said refrigeration subsystem is in thermal communication with at least one of the components of the electrical subsystem and at least one of the components of the electronic control subsystem, and wherein said electrical subsystem is in thermal communication with at least one of the components of the refrigeration subsystem and in electronic communication with at least one of the components of said electronic control subsystem, and wherein said electronic control subsystem is in electronic communication with at least one of the components of the electrical subsystem and at least one of the components of the refrigeration system. The refrigerant can be any phase change working fluid, as defined in ASHRAE Standard 34, that transfers heat; such as halogenated compounds (CFC""s) of the methane, ethane, and propane series, cyclic organic compounds, zeotropes, azeotropes, nitrogen compounds, inorganic compounds and elements such as water, and unsaturated organic compounds.